The present invention relates generally to cooling devices and, more particularly, to a cooling device and method for removing heat from an electronic device.
Electronic components, such as integrated circuits, are increasingly being used in different devices. One prevalent example of a device using integrated circuits is the computer. The central processing unit or units of most computers, including personal computers, is typically constructed from a plurality of integrated circuits. Integrated circuits are also used in other computer circuitry. For example, interface and memory circuits typically comprise several integrated circuits.
During normal operation, many electronic components, such as integrated circuits, generate significant amounts of heat. If this heat is not continuously removed, the electronic component may overheat, resulting in damage to the component and/or a reduction in its operating performance. For example, an electronic component may encounter thermal runaway, which may damage the electronic component. In order to avoid such problems caused by overheating, cooling devices are often used in conjunction with electronic components.
Over the years, the amount of heat generated by electronic components has increased. In addition, the size of electronic devices using these components has generally decreased, resulting in greater amounts of heat being generated within smaller confines. In order to adequately cool these hotter electronic devices without increasing their sizes, more efficient cooling devices are required.
One such cooling device used in conjunction with electronic components is a heat sink. A heat sink is a device that draws heat from a heat generating component and convects the heat to the surrounding atmosphere. The heat sink is typically formed from a thermally conductive material, such as aluminum or copper. The heat sink is usually placed on top of, and in physical contact with, the heat generating electronic component. This physical contact improves the thermal conductivity between the electronic component and the heat sink and permits heat to rise from the electronic component into the heat sink. In addition, a thermally conductive compound is typically placed between the electronic component and the heat sink to enhance to thermal conductivity between the electronic component and the heat sink. This thermal conductivity results in a substantial portion of the heat generated by the electronic component being conducted into the heat sink and away from the electronic component. The heat transfers to the surface of the heat sink where it is then convected into the surrounding atmosphere.
One method of increasing the cooling capacity of heat sinks is by including a plurality of cooling fins attached to the heat sink and a cooling fan that forces air past the cooling fins. The cooling fins serve to increase the surface area of the heat sink and, thus, increase the convection of heat from the heat sink to the surrounding atmosphere. The fan serves to force air past the fins, which further increases the convection of heat from the heat sink to the surrounding atmosphere. This increased convection, in turn, allows the heat sink to draw more heat from the electronic component. In this manner, the heat sink is able to draw a significant amount of heat away from the electronic component, which serves to cool the electronic component. Examples of such heat sinks are disclosed in U.S. Pat. No. 5,794,685 of Dean for HEAT SINK DEVICE HAVING RADIAL HEAT AND AIRFLOW PATHS and U.S. patent application Ser. No. 09/253877 of Hanzlik, et al. for COOLING APPARATUS FOR ELECTRONIC DEVICES, both of which are hereby incorporated by reference for all that is disclosed therein.
The amount of heat that may be drawn from a steady state heat source is dependent on the amount of heat that may be convected into the surrounding atmosphere. The amount of heat that may be convected into the surrounding atmosphere is, in turn, dependent on the surface area of the cooling fins and other components comprising the heat sink that convect heat to the surrounding atmosphere. For example, cooling fins with larger surface areas are generally able to convect more heat into the atmosphere.
Cooling fins with larger surface areas, however, tend to have significant barrier layers of air on the cooling fin surfaces when air is forced past the cooling fins. An air barrier is air that is adjacent the surface of a cooling fin and remains relatively stationary relative to the cooling fin as air is forced past the cooling fin. Thus, a significant barrier layer of air may result in the air being forced past cooling fins having large surface areas not being able to remove the maximum heat possible from the cooling fins. Accordingly, increasing the area of individual cooling fins may not result in a proportional cooling capability of the heat sink.
Another problem associated with larger cooling fins is that they occupy greater spaces, which could otherwise be used to reduce the size of the electronic device. Larger cooling fins also occupy space that could otherwise be used to increase the concentration of electronic components located within the electronic device. As described above, electronic components are being used in smaller devices, thus, a reduced space or a higher concentration of electronic components within the electronic devices is beneficial. The use of larger cooling fins tends to increase the size of the electronic devices or reduce the concentration of electronic components located therein.
Yet another problem associated with cooling fins is that they tend to be difficult to manufacture. For example, the cooling fins should be relatively thin in order to increase convection by providing less restrictive airflow past the fins. It should be noted that the thickness of the cooling fins must be balanced against their ability to conduct heat because thin cooling fins are generally unable to conduct from the heat sink as well as large cooling fins. The fin thins may, as an example, be made from a sheet of thermally conductive metal, such as a sheet of copper or aluminum. These cooling fins, however tend to be difficult to attach to the heat sink so as to assure low thermal resistance between the cooling fins and the heat sink. They may, as an example, be welded or brazed to the heat sink, which is relatively time consuming. Alternatively, the cooling fins may be integrally formed with the heat sink. For example, the heat sink, including the cooling fins may be molded or machined from a piece of stock. Molding or machining thin cooling fins, however, tends to be rather difficult and costly.
Thus, it would be generally desirable to provide a cooling device that overcomes these problems associated with conventional cooling devices.
An improved cooling device for dissipating heat from a heat source is disclosed herein. The cooling device may comprise an elongated core made of a thermally conductive material, such as copper or aluminum. The core may have an outer peripheral surface and an end that may be adapted to contact the heat source. At least one cooling fin device may be placed adjacent the outer peripheral surface of the core to enhance the convection of heat from the core to the surrounding atmosphere. Each cooling fin device may comprise at least one inner peripheral surface and at least one cooling fin associated therewith, wherein the inner peripheral surface of the cooling fin device is located adjacent the outer peripheral surface of the core. The area of the individual cooling fins may be small so as to reduce a barrier layer of air that builds up on the surface of the individual cooling fins when air is forced past the cooling fins. A plurality of relatively small cooling fins may be associated with the core via the cooling fin assemblies, thus, the overall surface area of the plurality of cooling fins may be relatively large, which improves convection of heat to the surrounding atmosphere.
The collars of the cooling fin devices may have inner surfaces that have substantially the same perimeter as the core. This allows the cooling fin devices to be pressed onto the core so as to form interference fits between the cooling fin devices and the core. The interference fits provide low thermal resistance between the cooling fin devices and the core, which improves the cooling capability of the cooling device by improving the thermal conductivity between the core and the cooling fin devices.
A conventional fan may be located in the vicinity of the core opposite the heat source and may serve to force air past the surfaces of the cooling fins in order to increase convection. The fan may force air in the general direction of the heat source in order to further increase the cooling capability of the cooling device. A shroud may be placed over the fan and the cooling fins to assure that air blown by the fan passes over the surfaces of the cooling fins rather than diverging from the core and the cooling fins.
The cooling fins may be relatively thin so as to minimize air resistance. Thus, a large quantity of air may be forced past the cooling fins, which in turn convects a large quantity of heat to the surrounding atmosphere. The cooling fins may, however, be thick enough so as to be able to draw a significant amount of heat from the core.
When the cooling device is used to dissipate heat generated by a heat generating electronic component mounted to a circuit board, the core is placed adjacent the electronic component. Heat is drawn from the electronic component into the core and away from the electronic component. The heat then transfers to the surface of the core and to the cooling fins. The air forced past the cooling fins by the fan convects the heat to the surrounding atmosphere, thus, cooling the electronic component. The elongated shape of the core allows for heat to be drawn primarily normal to the printed circuit board. Thus, the cooling device may occupy minimal area, which allows a higher concentration of electronic components to be mounted to the printed circuit board.